Two 12V inputs to one 12V output

Thread Starter

denalibeast

Joined Jan 2, 2020
4
Hello everyone this is my first post and I'm trying to figure out what diodes to use on a vehicle application including how I should setup the circuit, basically it's going to have two power sources, for instance, one from the vehicles DRL and one from the parking lights, in addition, the current circuit is setup like this, when the car is in drive it it turns on the DRL and when I switch on the parking lights the DRL power is cut, however, I want to have it when either the DRL is on or the parking lights are on the power is going to a LED bar on the headlight assembly. Both power sources have one 12V positive and negative.

Thanks in advance!
 

Thread Starter

denalibeast

Joined Jan 2, 2020
4
Are either the pos. common or the neg. common?
Light bar current requirement ?
Okay I'm still learning, so far I tried to tap into the positive on the DRL and the Parking light just tapped into both including putting one diode (1N4004 400V 1A DO-41 Axial Lead Rectifier Diode ) coming from each wire joining them both together at the end, but it did not light it up, however, lets assume that the power requirement is 12v for the light bar, in addition, I have no idea what the current requirement is other than it having two wires, one positive and one negative and currently I have it working connected to the parking lights, although, I would like it to be connected to both power sources so when the parking lights are off and the stock DRL is on then it would use power from the DRL instead, but keep it from bleeding over to the parking lights.

Here is the link for the lights I have https://www.amazon.com/1999-2006-Sierra-Projector-Headlights-Passenger/dp/B07CMK4M65
 

Bernard

Joined Aug 7, 2008
5,524
As a quick test, parking light + to anode of diode & light bar + to cathode ( white band ), both - s tied together. Does bar light?
 

Thread Starter

denalibeast

Joined Jan 2, 2020
4
As a quick test, parking light + to anode of diode & light bar + to cathode ( white band ), both - s tied together. Does bar light?
I will have to check when it stops raining like crazy, I don't have a garage, but last time I tried this and it didn't light up, now I don't know if I did it wrong or maybe I did too many diodes but the light bar did not come on with the parking lights on or the DRL on.Diagram.png
 

andrewmm

Joined Feb 25, 2011
323
that looks right to me,
Be careful how much current the lighting bar takes , The diodes can only take about an amp max, and drop 0.6 volts, so at full current dissipate 600 mW

If power is a problem, an alternative , is to use the diode OR you have to drive a relay , and the contacts of the relay used to power the light bar.
 
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